Light source device including semiconductor lasers

ABSTRACT

A cost-effective and accurate light source deice for use in an image forming apparatus and including semiconductor lasers is disclosed. The device needs only a minimum number of parts, obviates displacements during assembly, and allows collimator lenses to be adhered by photo-curable adhesive. Even when temperature around the device varies, the distance between the semiconductor lasers in a beam pitch direction varies little.

This application is a Continuation of application Ser. No. 09/055,902Filed on Apr. 7, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to a light source device for use in animage forming apparatus and including a semiconductor laser,particularly a plurality of semiconductor lasers.

A light source device including a semiconductor laser and a collimatorlens is extensively used in a digital copier, laser printer, facsimileapparatus or similar image forming apparatus. As for opticalcharacteristics, the light source device is required to have thedirectionality (optical axis characteristic) and parallelism(collimation characteristic) of a laser beam to issue from the device.To satisfy such characteristics, it is a common practice to adjust theemission point of the laser and the collimator lens relative to eachother in the directions of three axes x, y and z. The requiredpositional accuracy is less than the order of micron. Therefore, thelight source device of the type described should be adjustable inposition in the three directions x, y and z and should be fixed in placeat its adjusted position.

Adhesive used to affix the collimator lens contracts during curing. Itis therefore necessary to reduce the adverse influence of thecontraction on the optical characteristics. Particuarly, the accuracy ofthe light source device is severely restricted in the direction z(optical axis direction), so that the device must be so constructed asto obviate the contraction in the direction z. It is thereforepreferable that the adhesive layer be substantially parallel to theoptical axis or z axis, and that the contraction be limited to one ofthe x axis direction and y axis direction in order to facilitateadjustment.

Light source devices using a semiconductor laser and a collimator lensare taught in, e.g., Japanese Patent Laid-Open Publication Nos. 5-88061,5-136952, and 5-273483. The conventional light source devices, however,have some problems left unsolved, as follows.

(1) The devices are expensive because they need a number of parts.

(2) Displacements occur in the three directions x, y and z duringassembly, lowering the accuracy of directionality of the laser.

(3) To affix the collimator lens, use cannot be made of photo-curableadhesive capable of curing rapidly in a desired configuration and havinghigh reliability.

On the other hand, a multibeam scanning device capable of scanning aphotoconductive element with a plurality of laser beams is availablewith a digital copier, laser printer or similar image forming apparatus.This type of scanning device includes a plurality of semiconductorlasers arranged in the subscanning direction. Laser beams issuing fromthe lasers are so combined as to lie on optical axes adjoining eachother, and then output in one direction. A light source device for usein such a scanning device is, of course, required to have an accuratebeam pitch, i.e., distance between the laser beams in the direction y.

Light source devices for emitting a plurality of laser beams aredisclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-181410and 7-181412. However, the devices taught in these documents have thefollowing problem (4) in addition to the problems (1)-(3).

(4) The beam pitch of the semiconductor lasers cannot be accuratelymaintained due to the variation of temperature around the light sourcedevice.

The conventional light source devices have problems to be discussedlater in addition to the problems (1)-(4).

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acost-effective and accurate light source device needing a minimum numberof parts, obviating displacements during assembly, and allowingcollimator lenses to be affixed by photo-curable adhesive.

It is another object of the present invention to provide a light sourcedevice allowing a minimum of variation to occur in the distance betweensemiconductor lasers in the beam pitch direction even when temperaturearound the device varies.

In accordance with the present invention, a light source device includesa base formed with a plurality of through bores. A plurality ofsemiconductor lasers are positioned at the rear side of the base, andeach is received in the respective through bore of the base. A pluralityof collimator lenses are respectively adhered to a plurality of lenssupport portions formed on the front side of the base. The collimatorlenses each is positioned coaxially with the optical axis of therespective semiconductor laser. A plurality of apertures each shapes alaser beam to issue from the respective collimator lens. A beamcombining optical element combines laser beams to respectively issuefrom the semiconductor lasers to thereby output laser beams lyingsubstantially on a single optical axis. The lens support portions eachhas a center line extending substantially perpendicularly to a beampitch direction of the laser beams output from the collimator lenses.

Also, in accordance with the present invention, a light source device ismade up of a plurality of semiconductor lasers, a base formed withthrough bores for respectively press-fitting the semiconductor lasers, aplurality of lens support portions formed on the base, a plurality ofcollimator lenses respectively adhered to the lens support portions viaadhesive layers, an optical element for combining laser beams outputfrom the collimator lenses to thereby produce beams adjoining eachother, and a case mounted to the base for covering the collimator lensesand optical element. The adhesive layers each has a center thereofshifted outward of the respective bore in a beam pitch direction, sothat the adhesive layers each thermally expands inward.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptiontaken with the accompanying drawings in which:

FIG. 1 is a section showing a conventional light source device;

FIG. 2 is an exploded perspective view showing another conventionallight source device;

FIG. 3 is an exploded perspective view showing a first embodiment of thelight source device in accordance with the present invention;

FIG. 4 is a front view showing lens support portions included in thefirst embodiment for supporting collimator lenses;

FIG. 5 is an exploded perspective view showing a second embodiment ofthe present invention;

FIG. 6 is a front view showing lens support portions included in thesecond embodiment for supporting collimator lenses;

FIG. 7 is an exploded perspective view showing a third embodiment of thepresent invention;

FIG. 8 is a front view showing a method of affixing collimator lenses toa base included in the third embodiment;

FIG. 9A is a perspective view showing a base representative of a fourthembodiment of the present invention;

FIG. 9B is a front view of the base of FIG. 9A;

FIG. 10 is a front view showing a modification of the fourth embodiment;

FIG. 11 is an exploded perspective view showing a fifth embodiment ofthe present invention;

FIG. 12 is an exploded perspective view showing a sixth embodiment ofthe present invention;

FIG. 13 is a perspective view of the sixth embodiment;

FIG. 14 is a front view of the sixth embodiment;

FIG. 15 is an exploded perspective view showing a seventh embodiment ofthe present invention;

FIG. 16 is a perspective view showing a base included in the seventhembodiment;

FIG. 17 is a front view of the base of FIG. 16;

FIG. 18 is an exploded perspective view showing an eighth embodiment ofthe present invention;

FIG. 19 is a perspective view showing a base included in the eighthembodiment;

FIG. 20 is a front view of base shown in FIG. 19;

FIG. 21 is a vertical section showing a ninth embodiment of the presentinvention;

FIG. 22 is an exploded perspective view showing a tenth embodiment ofthe present invention;

FIG. 23 is a perspective view of a base included in the tenthembodiment;

FIG. 24 is a front view of the base of the tenth embodiment;

FIG. 25 is a partly taken away bottom view of the base included in thetenth embodiment;

FIG. 26 is an exploded perspective view showing in eleventh embodimentof the present invention;

FIG. 27 is a perspective view showing a twelfth embodiment of thepresent invention;

FIGS. 28A and 28B each shows a specific arrangement of notches formed ina base included in the twelfth embodiment;

FIG. 29 is a front view showing a thirteenth embodiment of the presentinvention;

FIG. 30 is a section along line A—A of FIG. 29;

FIG. 31A is an enlarged front view showing an adhesive layer included inthe thirteenth embodiment;

FIG. 31B shows directions in which the adhesive layer of FIG. 31Aexpands;

FIG. 31C demonstrates a condition wherein the expansion of the base andthat of the adhesive layer cancel each other and appear in the distancebetween collimator lenses;

FIG. 32 is a perspective view of a case representative of a fourteenthembodiment of the present invention;

FIG. 33 is a horizontal section showing a base also included in thefourteenth embodiment;

FIG. 34A is a section showing a fifteenth embodiment of the presentinvention;

FIG. 34B is a front view of a base included in the fifteenth embodiment;and

FIGS. 35A and 35B are fragmentary views showing a sixteenth embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the present invention, reference will be made to aconventional light source device including a semiconductor laser and acollimator lens, shown in FIG. 1. The light source device to bedescribed is taught in Japanese Patent Laid-Open Publication No. 5-88061mentioned earlier and emits a single laser beam. As shown, the deviceincludes a base 101 formed with a stepped hole 102. A semiconductorlaser 103 is press-fitted in the stepped hole 102. A flange 105 isfastened to the base 101 by two screws 104 and formed with a throughbore 106 aligning with the stepped hole 102. The left end of the bore106, as viewed in FIG. 1, is implemented as an inlet portion 106 agreater in diameter than the other portion by about 0.1 mm. A hollowcylindrical lens holder 107 is received in the bore 106, but spaced fromthe wall of the bore 106 by about 0.01 mm to 0.03 mm. A collimator lens108 is held in the lens holder 107 for converting a laser beam to aparallel beam.

A printed circuit board 109 is formed with a positioning hole 110. Aguide pin 111 protrudes from the end face of the base 101 and isreceived in the hole 110. The tip of the guide pin 111 is melted by heatand crushed thereby, as indicated by a phantom line 11′, therebyaffixing the base 101 and printed circuit board 109 to each other. Leads112 extending out from the laser 103 are passed through holes formed inthe circuit board 109 and soldered to a wiring pattern provided on therear of the circuit board 109.

The flange 105 is positioned in the directions x and y such that theemission point of the laser 103 aligns with the optical axis of thecollimator lens 108. Thereafter, the flange 105 is affixed to the base101 by the screws 104. The flange 105 is formed with a notch 113communicated to the inlet portion 106 a. After the lens holder 107 hasbeen adjusted in the direction x so as to bring the light sourceposition of the laser 103 into alignment with the focus of thecollimator lens 108, adhesive is filled in the bore 106 via the notch113 in order to affix the lens holder 107 to the flange 105.

An aperture forming member 114 is a shield cap for separating andshaping only the center portion of the beam output from the collimatorlens 108. The member 114 is formed with an aperture 114 a for selectingthe above portion of the beam and a lug 114 b mating with the flange113. In this condition, the member 114 is affixed to the flange 105.

When the above light source device is mounted to, e.g., the body of adigital copier or that of a laser printer, a flat surface 105 a includedin the flange 105 and perpendicular to the optical axis is used as areference surface. In addition, the surface 105 serves as a referencesurface for the adjustment of optical characteristics.

The laser beam issuing from the laser 103 is collimated by thecollimator lens 108. The center portion of the resulting parallel beamis passed through the aperture 114 a of the aperture forming member 114.The beam output via the aperture 114 a is incident to a photoconductiveelement via a polygonal mirror or similar deflector and an f-theta lensor similar optical element so as to form an image on the photoconductiveelement, although not shown specifically.

The light source device having the above configuration has the followingproblems (1)-(6).

(1) The adjusting portion assigned to the directions x and y (opticalaxis characteristic) and the adjusting portion assigned to the directionz (collimation characteristic or focal direction) each has anindependent structure. This increases the number of parts and the costof the device.

(2) The laser beam issuing from the laser 103 has a certain spread andis not always entirely incident to the collimator lens 108.Semiconductor lasers are standardized by laws from the safetystandpoint. A beam issuing from a semiconductor laser should preferablybe prevented form leaking in directions other than the direction of theoptical axis, not only during actual operation but also duringadjustment. That is, the flange 105 and base 101 must be formed ofmaterials capable of shielding the laser beam.

(3) The adhesive used to affix the lens holder 107 should advantageouslybe implemented by ultraviolet (UV)-curable adhesive. UV-curable adhesivecures rapidly and reduces the production tact and is reliable. However,because the base 101 and flange 105 are opaque for UV rays, UV raysradiated via the clearance filled with the UV-curable adhesive cannot beevenly incident to the entire adhesive, resulting in irregular curing orlocal curing. Consequently, a strain ascribable to contraction acts onthe assembly unevenly and displaces the lens holder 107 and causes thestructural elements to crack. A material opaque for infrared rays, redlight or similar laser beam is also opaque for UV rays shorter inwavelength than the laser beam. To allow such a material to transmitonly UV rays, it is necessary to add a special filter to the assembly orprovide the flange 105 itself with a special coating. This noticeablyincreases the cost of the assembly. It follows that the adhesive foraffixing the collimator lens 108 cannot be implemented by UV-curableadhesive.

(4) The adhesive exists on the entire circumference of the lens holder107, i.e., in the directions x, y and z. Therefore, the contraction ofthe adhesive during curing is not definite in the directions x or y,resulting in a scatter in the positional accuracy in the directions xand y. To guarantee positional accuracy after adhesion, it is necessaryto provide the initial position with some offset taking account of thecontraction. However, if the directions of contraction are not constant,it is difficult to provide the initial position with an offset andprevent accuracy in the directionality of the laser (optical axischaracteristic) from falling.

(5) After the adjustment in the directions x and y, the flange 105 isaffixed to the base 101 by the screws 104. This is undesirable becausescrew seats formed on the end face of the base 101 and the flange 105bite each other when the screws 104 are driven. As a result,displacements in the directions x and y are apt to occur and lower theaccuracy of the directionality of the laser.

(6) Because the adhesive is introduced into the clearance via the notch23, a strain and therefore a scatter in the positional accuracy occursdue to the partial contraction of the adhesive during the inflow of theadhesive or the irregular flow of the adhesive.

FIG. 2 shows a light source device of the type emitting a plurality of(two) beams and taught in each of Japanese Patent Laid-Open PublicationNos. 7-181410 and 7-181412 also mentioned earlier. As shown, the lightsource device includes two bases 201 each having a stepped hole like thebase 101 of FIG. 1. Two semiconductor lasers 203 are respectivelypress-fitted in the two stepped holes. The bases 201 are fastened to aflange 205 by four screws 204. Through bores 205 a are formed in theflange 205 in alignment with the semiconductor lasers 203. Hollowcylindrical lens holders 207 each is received in the respective bore 205a, but spaced from the wall of the bore 205 a by about 0.01 mm to 0.03mm. Each lens holder 207 has a collimator lens 208 thereinside forconverting a laser beam to a parallel beam. The bases 201 each isadjusted in the directions x and y such that the emission point of therespective laser 203 aligns with the optical axis of the associatedcollimator lens 208. Then, the bases 201 are affixed to the flange 205by the screws 204.

The bores 205 a of the flange 205 each is formed with notches 206 a.After the lens holders 207 have been so adjusted in the direction z asto bring the emission points of the lasers 203 into alignment with thefocuses of the associated collimator lenses 208, adhesive is fed via thenotches 206 a in order to affix the lens holders 207 to the flange 205.

Aperture forming members 209 each separates and shapes the center partof the beam output from the associated collimator lens 208. Eachaperture forming member 209 is formed with an aperture 209 a aligningwith the optical axis of the parallel beam output from the associatedcollimator lens 208. The parallel beams output from the apertures 209 aare combined by a beam combining prism 210 to turn out beams 211existing on substantially the same optical axis. The angles of theoutput optical axes are finely adjusted such that the two beams 211 havea pitch implementing a desired pitch in the subscanning direction on animage forming plane (i.e., pitch in the direction of lines in the caseof simultaneous two-line writing). This method corresponds to theadjustment of the bases 201 in the direction y.

As shown in FIG. 2, the aperture forming members 209 and prism 210 arereceived in a case 212. The case 212 is positioned by the bores 205 a ofthe flange 205 and positioning portions, not shown, included in the case212, and then affixed to the flange 205 via screw holes formed in itsfour corners. The flange 205 is formed of metal (particularly aluminum)in order to prevent the heat radiation of the lasers 203 and theadjusted beam pitch from being effected as far as possible. The case 212is implemented as a resin molding from the cost standpoint.

The light source device shown in FIG. 2 has the following problems(1)-(3).

(1) The characteristic of the adhesive after curing is equivalent to thecharacteristic of resins in general. Usually, the coefficient of linearexpansion of resin becomes greater than that of metal, causing resin tocontract noticeably in the event of temperature variation. Even when thebases 201 and flange 205 are formed of metal having a small coefficientof linear expansion, the adhesive layers intervening between thecollimator lenses 208 cause the pitch or distance between the lenses 208to vary noticeably when temperature varies. This varies the angles ofthe beams 211 output from the prism 210 and the distance between themand therefore the pitch on the image writing plane in the subscanningdirection, thereby deteriorating image quality.

(2) The adhesive layers exist on the entire circumferences of thecollimator lenses 208. Therefore, when each collimator lens 208 adjustedin the direction z (collimation characteristic) is affixed by theadhesive, it is displaced due to contraction in both of she directions xand y. As a result, the positional accuracy (optical axis accuracy) ofeach lens 208 varies in the directions x and y after the adhesive hascured. To adjust the distance between the two beams 211 with higheraccuracy, it is necessary to loosen the screws of either one of thebases 201 after the fixation of the lenses 208, again adjust theposition in the directions x and y (particularly y), and then drive thescrews in order to affix the base 201 to the flange 205. However, whilethe required accuracy in the direction z (collimation characteristic orfocal direction) is less than the order of micron, a stress occurs inthe direction z in the event of fastening and brings about adisplacement of the order of micron in the direction z. Consequently,this method degrades accuracy in the direction z although implementingaccurate adjustment of the distance between the beams. That is, when thedistance between the beams is varied on an image plane due to, e.g., thescatters of optical parts other than the light source device, and if itis adjusted via the light source device, accuracy in the direction z isdeteriorated.

(3) The lasers 203 each is affixed to the respective base 201 which is,in turn, fastened to the flange 205 by the respective two screws 204.Then, the flange 205 is fastened to the case 212 by screws. This isundesirable because each part is apt to deform or move due to thefastening force, causing the beam pitch to vary.

Preferred embodiments of the light source device in accordance with thepresent invention will be described hereinafter.

1st Embodiment

Referring to FIGS. 3 and 4, a light source device embodying the presentinvention is shown and includes a base 41 formed with two through bores41 a. Two semiconductor lasers 42 are respectively press-fitted in therear parts of the bores 41 a. In the illustrative embodiment, twocollimator lenses 43 are directly adhered to the base 41. Specifically,lens support portions 41 b are molded integrally with the front of thebase 41, and each has an arcuate section slightly greater in diameterthan the collimator lenses 43. The diameter of each lens support portion41 b may be about 0.2 mm. The lens support portions 41 b each has anaxis aligning with the optical axis of the associated laser 42. Ifdesired, each lens support portion 41 may be provided with an arcuatesection slightly greater in the radius of curvature than the collimatorlens 43 by the thickness of an adhesive layer.

The lens support portions 41 b each has a length, as measured in thedirection of the optical axis (direction z), greater than the thicknessof the collimator lens 43 (direction z), so that excess adhesive isprevented from deposing on unexpected portions. The portions 41 b eachhas an arcuate section smaller than a semicircle, as seen in a frontview. As shown in FIG. 4, the arcuate section should preferably extendover about 60 degrees and be symmetrical in the right-and-left directionwith respect to a center line C in order to facilitate positionadjustment and adhesion. The center lines C of the lens support portions41 b are substantially perpendicular to the subscanning pitch direction(direction y) of the two beams to issue from the collimator lenses 43.

The collimator lenses 43 are transparent for UV rays. While plastics andglass, for example, are transparent for UV rays, glass is desirable fromthe optical characteristic standpoint. As shown in FIG. 4, duringassembly, each collimator lens 43 is held by a chuck 47 movable in thethree directions x, y and z and then positioned on the respective lenssupport portion 41 b coaxially with the associated laser 42.

UV-curable adhesive 46 is filled in a gap formed between the adhesionsurface 41c of each support portion 41 b and the circumference of theassociated collimator lens 43. Subsequently, the collimator lens 43 isfinely adjusted to its position implementing an expected opticalcharacteristic, and then the chuck 47 is fixed in place. Thereafter, asshown in FIG. 4, UV rays L are radiated from a UV radiator 48 toward theadhesive 46 from above the collimator lens 43. The UV rays L areincident to the adhesive 46 via the collimator lens 43 and causes it tocure evenly.

The curing of the adhesive is effected with each of the two collimatorlenses 43. As a result, an adhesive layer 46 is formed between theadhesion surface 41 c of each lens support portion 41 b and theassociated collimator lens 43. The adhesive layer 46 is therefore about0.2 mm thick and symmetrical in the right-and-left direction and has athickness in the direction substantially perpendicular to thesubscanning pitch direction (direction y). Each collimator lens 43 isaffixed to the respective lens support portion 41 b by the adhesivelayer 46 while Preserving its expected optical characteristic. That is,the lens support portions 41 b are symmetrical with respect to a lineperpendicular to the beam pitch direction.

Particularly, each lens support portion 41 b has a symmetrical arcuatesection extending over about 60 degrees, as shown in FIG. 4. Such aconfiguration allows the chuck 47 to chuck the collimator lens 43 surelyand easily. In addition, the UV rays L issuing from the UV radiator 48can illuminate the entire adhesion surface 41 c via the collimator lens43, insuring the even and complete curing of the adhesive. The fully setuniform adhesive layer obviates the displacement of the collimator lens43 ascribable to irregular curing or local curing.

Because strains ascribable to the contraction of the adhesive occursymmetrically in the right-and-left direction and cancel each other, astrain occurs only in the direction x. The strain in the direction x canbe provided with fine offset taking account of the contraction of theadhesive. It follows that the beams output from the two collimatorlenses 43 have desirable directionality (optical axis characteristic) inthe direction y, and of course have an accurate beam pitch (accuracy inthe distance in the direction y or subscanning direction).

In addition, because each adhesive layer is symmetrical in theright-and-left direction or direction y, the expansion and contractionof the adhesive layer ascribable to the ambient temperature is cancelledin the direction y, i.e., limited to the direction x. This furtherenhances the accuracy of the distance between the two beams.

As shown in FIG. 3, an aperture forming member 44 is used to select thecenter portion of the parallel beam output of each collimator lens 43.For this purpose, the aperture forming member 44 is formed with twoapertures 44 a respectively aligning with the optical axes of thecollimator lenses 43. The parallel beams output from the two apertures44 a are combined by a beam combining prism, or beam combining means, 45to turn out beams existing on substantially the same axis. The combinedbeams are incident to scanning optics, not shown, for writing an image.The angles of the output optical axes are finely adjusted such that thetwo beams have a pitch implementing a desired pitch in the subscanningdirection on an image forming plane (i.e., pitch in the direction oflines in the case of simultaneous two-line writing). This methodcorresponds to the adjustment of the collimator lens 43 in the directiony. If desired, the beam combining means may be implemented by acombination of a mirror and a half-mirror.

The aperture forming member 44 and prism 45 are mounted to the base 41by a mounting member, not shown. At this instant, two contiguouscircular stepped portions 41 d are used for positioning while four holes41 e are used for mounting.

As stated above, the illustrative embodiment achieves variousunprecedented advantages, as enumerated below.

(1) The center line C of each lens support portion 41 b is substantiallyperpendicular to the direction of the pitch of two beams output from thecollimator lenses 43 (direction y). Therefore, the influence ofcontraction of the adhesive 46 due to curing does not act in the abovebeam pitch direction. This, coupled with the fact that the influence ofexpansion and contraction of the adhesive 46 ascribable to the varyingtemperature does not act in the beam pitch direction, provides the lightsource device with an accurate beam pitch and allows it to preserve itsaccuracy stably.

(2) The collimator lenses 43 each is directly affixed to the respectivelens support portion 41 b molded integrally with the base 41. Therefore,the number of parts and therefore the cost of the light source device isreduced. Further, because holders or similar members do not intervenebetween the collimator lenses 43 and the lens support portions 41 b, thedevice is free from the influence of the errors of such intermediarymembers. In addition, directly affixing the lenses 43 to the lenssupport members 41 b obviates the need for screws or similar fasteningmeans. The device is therefore free from displacements particular tofastening.

(3) The lens support portions 41 b are symmetrical with respect to aline perpendicular to the beam pitch direction, so that strainsascribable to the contraction in the beam pitch direction cancel eachother. This limits the contraction to the direction perpendicular to thebeam pitch direction and thereby further enhances the directionality ofcontraction and therefore accurate position adjustment.

(4) The lens support portions 41 b each has an arcuate section whosediameter is slightly greater than the diameter of the collimator lens43. Therefore, when each lens support portion 41 b and associatedcollimator lens 43 are positioned coaxially with each other, theadhesive layer between them has a uniform thickness and can thereforecure evenly. This protects the collimator lenses 43 from displacement.The radius of curvature of each lens support portion 41 b greater thanthat of the collimator lens 43 by the thickness of the adhesive layerfurther enhances the above effect.

(5) Because each lens support portion 41 b has an arcuate sectionsmaller than a semicircle, the adhesive layer covers only less than onehalf of the circumference of the collimator lens 43 and gives thecontraction of the adhesive 46 directionality. The initial position ofthe collimator lens 43 can therefore be provided with an offset takingaccount of the contraction of the adhesive 46 to occur, enhancingpositional accuracy after the curing of the adhesive 46. In addition,light for curing the adhesive 46 can be directed toward the side ends ofthe collimator lenses 43 via the open sides of the lens support portions41 b, obviating irregular curing more positively.

(6) Gaps, grooves or similar non-adhesion portions prevent the adhesivefrom bridging the collimator lenses 43 and base 41 in the optical axisdirection. Therefore, even when the adhesive 46 is introduced in anexcessive amount, it is prevented from directly depositing on the wallsof the base 41 and exerting its contracting force on the collimatorlenses 43 in the direction z. This additionally increases the positionalaccuracy in the optical axis direction or direction z.

The UV-curable adhesive used in the above embodiment may be replacedwith any other photo-curable adhesive. Also, the light source device maybe so constructed as to emit three or more beams, as needed.

2nd Embodiment

Referring to FIGS. 5 and 6, a second embodiment of the light sourcedevice in accordance with the present invention is shown and includes afirst base 51 and a second base 54. The first base 51 is formed withthrough bores 51 a and 51 b. A semiconductor laser 52 a is press-fittedin the rear part of the bore 51 a. A collimator lens 53 a is directlyadhered to the first base 51. Specifically, a lens support portion 51 cis molded integrally with the front of the first base 51 and has anarcuate section slightly greater in diameter than the collimator lens 53a. The diameter of the lens support portion 51 c may be about 0.2 mm.The lens support portion 51 c has an axis aligning with the optical axisof the laser 52 a. The lens support portion 51 c has a length, asmeasured in the direction of the optical axis (direction z), greaterthan the thickness of the collimator lens 53 a (direction z), so thatexcess adhesive is prevented from deposing on unexpected portions.

The portion 51 c has an arcuate section smaller than a semicircle, asseen in a front view. The second base 54 is formed with a through bore54 a and a circular stepped portion 54 b. A semiconductor laser 52 b ispress-fitted in the rear part of the bore 54 a. A collimator lense 53 bis directly adhered to the second base 54. Specifically, a lens supportportion 54 c is molded integrally with the front of the base 54 and hasan arcuate section slightly greater in diameter than the collimator lens53 b. The diameter of the lens support portion 54 c may be about 0.2 mm.The lens support portion 54 c has an axis aligning with the optical axisof the laser 52 b. The lens support portion 54 c has a length, asmeasured in the direction of the optical axis (direction z), greaterthan the thickness of the collimator lens 53 b (direction z), so thatexcess adhesive is prevented from deposing on unexpected portions. Thebase 54 is temporarily positioned by the bore 51 b of the base 51 andthe stepped portion 54 b of the base 54, and then fastened to the base51 by two screws 55, holes 54 d, and threaded holes 51 d.

As shown in FIG. 6, the arcuate section of each of the lens supportportions 51 c and 54 c should preferably extend over about 60 degreesand be symmetrical in the right-and-left direction in order tofacilitate position adjustment and adhesion. The center lines C1 and C2of the arcuate lens support portions 51 c and 54 c, respectively, aresubstantially perpendicular to the subscanning pitch direction(direction y) of two beams to issue from the collimator lenses 53 a and53 b.

The collimator lenses 53 a and 53 b are transparent for UV rays. Whileplastics and glass, for example, are transparent for UV rays, glass isdesirable from the optical characteristic standpoint. As shown in FIG.6, during assembly, each collimator lens 53 a or 53 b is held by a chuck57 movable in the three directions x, y and z and then positioned on therespective lens support portion 51 c or 54 c coaxially with theassociated laser 52 a or 52 b.

UV-curable adhesive 56 a is filled in a gap formed between the adhesionsurface 51 e of the support portion 51 c and the circumference of thecollimator lens 53 a. Subsequently, the collimator lens 53 a is finelyadjusted to its position implementing expected optical characteristics,and then the chuck 57 is fixed in place. Thereafter, as shown in FIG. 6,UV rays L1 are radiated from a UV radiator 58 a toward the adhesive 56 afrom above the collimator lens 53 a. The UV rays L1 are incident to theadhesive 56 a via the collimator lens 53 a and causes it to cure evenly.

Adhesive 56 b intervening between the other adhesion surface 54 e andthe collimator lens 53 b is also caused to cure by UV rays issuing froma UV radiator 58 b.

As a result, an adhesive layer 56 a is formed between the adhesionsurface 51 c of the lens support portion 51 c and the collimator lens 53a. The adhesive layer 56 a is therefore about 0.2 mm thick andsymmetrical in the right-and-left direction and has a thickness in thedirection substantially perpendicular to the subscanning pitch direction(direction y). Likewise, an adhesive layer 56 b is formed between theadhesion surface 54 e of the lens support portion 54 c and thecollimator lens 53 b. The adhesive layer 56 b is identical withconfiguration with the adhesive layer 56 a. The collimator lens 53 a and53 b each is affixed to the respective lens support portion 51 c or 54 cby the adhesive layer while preserving its expected opticalcharacteristic. That is, the lens support portions 51 c and 54 c aresymmetrical with respect to a line perpendicular to the beam pitchdirection.

Particularly, each lens support portion 51 c or 54 c has a symmetricalarcuate section extending over about 60 degrees, as shown in FIG. 6.Such a configuration allows the chuck 57 to chuck each collimator lens53 a or 53 b surely and easily. In addition, the UV rays L1 and L2issuing from the UV radiators 58 a and 58 b, respectively, each canilluminate the entire adhesion surface 51 e or 54 e via the collimatorlens 53 a or 53 b, insuring the even and complete curing of theadhesive. The fully set even adhesive layer obviates the displacement ofthe collimator lens ascribable to irregular curing or local curing.

Because strains ascribable to the contraction of the adhesive occursymmetrically in the right-and-left direction and cancel each other, astrain occurs only in the direction x. The stain in the direction x canbe provided with fine offset taking account of the contraction of theadhesive. It follows that the beams output from the two collimatorlenses have desirable directionality (optical axis characteristic) inthe direction y, and of course have an accurate beam pitch (accuracy inthe distance in the direction y or subscanning direction). In addition,because each adhesive layer is symmetrical in the right-and-leftdirection or direction y, the expansion and contraction of the adhesivelayer ascribable to the ambient temperature is cancelled in thedirection y, i.e., limited to the direction x. This further enhances theaccuracy of the distance between the two beams.

After the collimator lens 53 b has been adhered to the second base 54,the base 54 can be adjusted in position in the directions x and y(particularly y) by loosening the screws 55. Therefore, when the beampitch or distance on an image surface differs from expected one due toan extrinsic scatter, it is possible to readjust the base 54, i.e., thebeam distance in any one of the directions x and y.

In the above embodiment, the second base 54 is fastened to the firstbase 51 first. Alternatively, after the collimator lens 53 b has beenadhered to the second base 54, the second base 54 may be affixed to thefirst base 51 carrying the collimator lens 53 a therewith. This will befollowed by the adjustment of the distance between the two beams.

As shown in FIG. 5, an aperture forming member 59 is used to select thecenter portion of the parallel beam output of each collimator lens 53 aor 53 b. For this purpose, the aperture forming member 59 is formed withtwo apertures 59 a and 59 b respectively aligning with the optical axesof the collimator lenses 53 a and 53 b. The parallel beams output fromthe two apertures 59 a and 59 b are combined by a beam combining prism,or beam combining means, 60 to turn out beams existing on substantiallythe same axis. The combined beams are incident to scanning optics, notshown, for writing an image. The angles of the output optical axes arefinely adjusted such that the two beams have a pitch implementing adesired pitch in the subscanning direction on an image forming surface(i.e., pitch in the direction of lines in the case of simultaneoustwo-line writing). This method corresponds to the adjustment of thecollimator lens in the direction y.

The aperture forming member 59 and prism 60 are mounted to the firstbase 51 by a mounting member, not shown. At this instant, the circularstepped portion 51 f of the first base 51 is used for positioning whilefour holes 51 g are used for mounting.

As stated above, the illustrative embodiment achieves the followingvarious advantages.

(1) The first base 51 is provided with the bore 51 a defining theoptical axis of at least one beam, the semiconductor laser 52 a receivedin the bore 51 a, the collimator lens 53 a coaxial with the laser 52 a,and the lens support portion 51 c also coaxial with the laser 52 a. Thesecond base 54 is provided with the through bore 54 a defining theoptical axis of another beam, the semiconductor laser 52 b received inthe bore 54 a, the collimator lens 53 b coaxial with the laser 52 b, andthe lens support portion 54 c also coaxial with the laser 52 b.Therefore, when a desired distance between the beams is not set up on animage writing surface due to, e.g., the scatter of any optical partother than the light source device, the distance can be adjusted withoutvarying the characteristic of the device in the direction z (collimationcharacteristic), thereby insuring desirable image quality.

(2) The collimator lenses 53 a and 53 b are respectively directlyaffixed to the lens support portions 51 c and 54 c molded integrallywith the bases 51 and 54. Therefore, the number of parts and cost of thelight source device are reduced. Further, because holders or similarmembers do not intervene between the collimator lenses 53 a and 53 b andthe lens support portions 51 c and 54 c, the device is free from theinfluence of the errors of such intermediary members. In addition,directly affixing the lenses 53 a and 53 b to the lens support members51 c and 54 c obviates the need for screws or similar fastening means.The device is therefore free from displacements ascribable to fastening.

(3) The lens support portions 51 c and 54 c are symmetrical with respectto a line perpendicular to the beam pitch direction, so that strainsascribable to the contraction in the beam pitch direction cancel eachother. This limits the contraction to the direction perpendicular to thebeam pitch direction and thereby further enhances the directionality ofcontraction and therefore accurate position adjustment.

(4) The lens support portions 51 c and 54 c each has an arcuate sectionwhose diameter is slightly greater than the diameter of the collimatorlens 53 a or 53 b. Therefore, when each lens support portion 51 c or 54c and associated collimator lens 53 a or 53 b are positioned coaxiallywith each other, the adhesive layer between them has a uniform thicknessand can therefore cure evenly. This protects the collimator lenses 53 aand 53 b from displacement. The radius of curvature of each lens supportportion 51 c or 54 c greater than that of the collimator lens 43 by thethickness of the adhesive layer further enhances the above effect.

(5) Because each lens support portion 51 c or 54 c has an arcuatesection smaller than a semicircle, the adhesive layer covers only lessthan one half of the circumference of the collimator lens 53 a or 53 band gives the contraction of the adhesive directionality. The initialposition of each collimator lens 53 a or 53 b can therefore be providedwith an offset taking account of the contraction of the adhesive tooccur, enhancing positional accuracy after the curing of the adhesive.In addition, light for curing the adhesive can be directed toward theside ends of the collimator lenses 53 a and 53 b via the open sides ofthe lens support portions 51 c and 54 c, obviating irregular curing morepositively.

(6) Gaps, grooves or similar non-adhesion portions prevent the adhesivefrom bridging the collimator lenses 53 a and 53 b and bases 51 and 54 inthe optical axis direction. Therefore, even when the adhesive isintroduced in an excessive amount, it is prevented from directlydepositing on the walls of the bases 51 and 64 and exerting itscontracting force on the collimator lenses 53 a and 53 b in thedirection z. This additionally increases the positional accuracy in theoptical axis direction or direction z.

The UV-curable adhesive used in the above embodiment may be replacedwith any other photo-curable adhesive. Also, the light source device maybe so constructed as to emit three or more beams.

3rd Embodiment

Referring to FIGS. 7 and 8, a third embodiment of the light sourcedevice in accordance with the present invention is shown and includes asubstantially rectangular flat base 1. Two through bores 1 a are formedsubstantially at the center of the base 11 and positioned side by sidein the direction y. Two semiconductor lasers 2 are respectivelypress-fitted in the rear parts of the bores 1 a. Two collimator lenses 3are directly adhered to the base 1. Specifically, lens support portions1 b are molded integrally with the front of the base 1, and each has anarcuate section slightly greater in diameter than the collimator lenses3. The diameter of each lens support portion 1 b may be about 0.2 mm.The lens support portions 1 b each has an axis aligning with the opticalaxis of the associated laser 2. The lens support portions 1 b each has alength, as measured in the direction of the optical axis (direction z),greater than the thickness of the collimator lens 3 (direction z), sothat excess adhesive is prevented from deposing on unexpected portions.The portions 1 b each has an arcuate section smaller than a semicircle,as seen in a front view.

As shown in FIG. 8, the arcuate section should preferably extend overabout 60 degrees and be symmetrical in the right-and-left direction inorder to facilitate position adjustment and adhesion. The center lines Cof the lens support portions 1 b are substantially perpendicular to thesubscanning pitch direction (direction y) of the two beams to be outputfrom the collimator lenses 3.

An aperture forming member 4 is formed with apertures 4 a each forselecting a light beam and is received in a case 9. A beam combiningoptical member 4 is implemented as a prism capable of combining twobeams 10 output via the apertures 4 a into beams existing substantiallyon the same axis. The optical member 4 is also received in the case 9.If desired, the optical member 4 may be implemented as a combination ofa mirror and a half-mirror.

As shown in FIG. 8, in the event of assembly, each collimator lens 3 isheld by a chuck 7 movable in the three directions x, y and z. The chuck7 positions the lens 7 on the associated lens support portion 1 bcoaxially with the optical axis of the associated laser 2. Subsequently,UV-curable adhesive is filled in a gap formed between the adhesionsurface the lens support portion 1 b and the circumference of thecollimator lens 3, forming an adhesive layer 6. Then, the collimatorlens 3 is finely adjusted to its position implementing an expectedoptical characteristic, and then the chuck 7 is fixed in place.Thereafter, as shown in FIG. 8, UV rays are radiated from a UV radiator8 toward the adhesive layer 6 from above the collimator lens 3. The UVrays are incident to the adhesive layer 6 via the collimator lens 3 andcause it to cure evenly. The curing of the adhesive is effected witheach of the two collimator lenses 3. As a result, the adhesive layer 46is formed between each lens support portion 1 b and the associatedcollimator lens 3. The adhesive layer 6 is therefore about 0.2 mm thickand symmetrical in the right-and-left direction and has a thickness inthe direction substantially perpendicular to the subscanning pitchdirection (direction y). Each collimator lens 3 is affixed to therespective lens support portion 1 b by the adhesive layer 6 whilepreserving its expected optical characteristic.

The adhesive layers 6 each has a length, as measured in the optical axisdirection smaller than the length of the associated lens support portion1 b, so that a gap is formed between the adhesive layer 6 and the base1. While the light source device is in operation, the adhesive layers 6expand due to temperature elevation. At this instant, should theadhesive layers 6 and base 1 be held in close contact with each other,the collimator lenses 3 would move in the optical axis direction due tothe expansion of the adhesive layers 6. The gap between each adhesivelayer 6 and the base 1 allows the layer 6 to freely move to both sidesof the associated lens 3 and prevents it from moving the lens 3.

The case 9 is positioned by positioning holes 1 c formed in the base 1and positioning recesses, not shown, formed in the case 9. After fourthreaded holes 9 a formed in the case 9 and four holes 1 d formed in thebase 1 have been aligned, the case 9 is fastened to the base 1 by fourscrews 11.

4th Embodiment

FIGS. 9A and 9B show a base 21 representative of a fourth embodiment ofthe present invention and including a single lens support portion 21 b.As for the rest of the construction, this embodiment is identical withthe third embodiment shown in FIG. 7.

Assume that the conventional light source device shown in FIG. 2 ismounted to a digital copier or a laser printer. Then, even if the deviceinitially has expected optical characteristics, the flange 205, forexample, deforms due to a stress ascribable to assembly or expansion andcontraction ascribable to temperature variation in the machine. Thisembodiment pertains to a light source device generally implemented asenlargement type optics. Therefore, even the slightest displacement ofany part ascribable to deformation would be enlarged on reaching awriting position assigned to a photoconductive element and would turnout a noticeable displacement, critically effecting the opticalcharacteristics. Particularly, deformation in the direction ydeteriorates the parallelism of the individual laser beam.

The fourth embodiment solves the above problem by allowing a minimum ofdeformation to occur in the light source device. Should the machine bodyfor accommodating the light source device be rearranged, other variousportions would be effected and would bring about extra costs. In thissense, the scarcely deformable structure is desirable.

As shown in FIGS. 9A and 9B, the base 21, like the base 1 of FIG. 7, hasthrough bores 21 a for receiving the semiconductor lasers 2. The base 21is characterized in that a single continuous lens support portion 21 bis substituted for the two lens support portions 1 b. Specifically, thelens support portion 21 b has two lens support portions 21 b 1 connectedto each other by a straight tie portion 21 b 2. The tie portion 21 b 2is substantially parallel to the beam pitch direction or direction y anduniform in thickness in the same direction. Notches 21 b 3 arerespectively formed between the lens support portions 21 b 1 and the tieportion 21 b 2, and each extends in the optical axis direction. Thenotches 21 b 3 prevent adhesive from reaching the tie portion 21 b 2when it is filled for affixing the collimator lenses 3. The lens supportportions 21 b 1 are symmetrical with each other with respect to the tieportion 21 b 2.

Because the tie portion 21 b 2 extends in the direction y, it preventsthe base 21 from deforming in the direction y and thereby effectivelyobviates errors in the distance between the two beams 10 and the angleof the individual beam.

FIG. 10 shows a base 22 representative of a modification of the fourthembodiment. As shown, a line connecting the optical axes of the twocollimator lenses 3 is inclined with respect to the y axis. Thedifference between the base 21, FIGS. 9A and 9B, having the lenses 3arranged in parallel to the axis y, and the base 22 stems from adifference in the structure of writing optics, although not describedspecifically. The base 22 includes a lens support portion 22 b which isalso inclined. The lens support portion 22 b is made up of two lenssupport portions 22 b 1 and a straight tie portion 22 b 2 connectingthem together. The tie portion 22 b 2 is slightly thinner than the tieportion 21 b 2, FIGS. 9A and 9B, and stepped, as illustrated. The tieportion 22 b 2 may be slightly inclined, a shown and described, althoughit will be most effective when extending in parallel to the y axis.

5th Embodiment

FIG. 11 shows a fifth embodiment of the present invention. Thisembodiment is essentially similar to the embodiment of FIG. 7; identicalstructural elements are designated by identical reference numerals andwill not be described in order to avoid redundancy. In the conventionalstructure shown in FIG. 2, the flange 205 is fastened to the case 212 bythe screws inserted into the four holes 205 b formed in the corners ofthe flange 205. This gives rise to a problem that if the flange 205 andcase 212 are different in the coefficient of linear expansion, then thetemperature elevation of the light source device distorts the flange 205and thereby disturbs the distance between the two beams 211 and theparallelism of the same (beam pitch accuracy).

In the illustrative embodiment, a single hole 1 d is formed in the base1 in the vicinity of the center of the base 1. A female threaded hole 1d is formed in the case 9. A screw 11 is driven into the threaded holeof the case 9 via the hole 1 d of the base 1, so that the base 1 isfastened to the case 9 at a single point.

In the above configuration, even when the base 1 and case 9 aredifferent in the coefficient of linear expansion, each of them canexpand and contrast independently of the other. This frees the base 1from distortion and insures the accurate beam pitch between the twobeams 10. The base 1 and case 9 each can be formed of any desiredmaterial and therefore implemented even as an inexpensive plasticmolding. Moreover, if the hole 1 d for the screw 11 is positioned on acenter line C′ intermediate between the center lines C of the lasers 2extending in the direction y, it is possible to protect the base 1 fromdeformation and to enhance the stability of the relative position of thebase 1 and case 9 during assembly, i.e., accurate beam pitch.

6th Embodiment

FIGS. 12-14 show a sixth embodiment of the present invention alsoconstituting an improvement over the conventional light source device ofFIG. 2. In the device shown in FIG. 2, the case 212 is mounted to theflange 205 after the optical element 210 has been mounted to the case212. This is undesirable because any positional error of the opticalelement 210 effects the pitch accuracy of the beams 211. Moreover, whilethe case 212 should preferably be implemented as an inexpensive plasticmolding, a plastic molding is noticeably susceptible to temperature.Particularly, the displacement of a plastic molding (especially in thebeam pitch direction) ascribable to expansion or contraction hascritical influence on accuracy. The sixth embodiment is a solution tosuch problems.

As shown in FIG. 12, the base 1 additionally includes an optical elementsupport portion 23 extending out from the opposite lens support portions1 b. An aperture forming member 14 is positioned downstream of theoptical element 5 in the direction of beam propagation and thereforeformed with a single aperture 14 a.

The optical element support portion 23 includes a reference surface 23 aand a surface 23 b, as illustrated. The optical element 5 is positionedby the reference surface 23 a and affixed to the surface 23 b by anadhesive layer 24 (see FIG. 14). In this configuration, even when theadhesive layer 24 expands or contracts due to temperature variation, nochanges occur in the direction y (beam pitch direction). The adhesiveshould preferably be reliable photo-curable adhesive and shouldpreferably be identical with the adhesive used to affix the collimatorlenses 3 from the easy production standpoint. Subsequently, thecollimator lenses 3 are positioned and then adhered, as described withreference to FIG. 8.

All of the semiconductor lasers 2, collimator lenses 3 and opticalelement 5 needing high positional accuracy are supported by the base 1,as stated above. With this configuration, it is easy to implementrequired assembly accuracy and maintain it. In addition, the opticalelement support portion 23 extends in the direction y and effectivelyobviates distortion in the direction y.

While the optical element support portion 23 has been shown anddescribed as being molded integrally with the lens support portions 1 b,it may be implemented as an independent member and mounted to the base1.

7th Embodiment

Referring to FIGS. 15-17, a seventh embodiment of the present inventionwill be described. In the conventional light source device shown in FIG.2, the aperture forming member 209 is mounted to the case 212 and thenmounted to the flange 205 together with the case 212. This brings abouta problem that any error in the position of the aperture 209 atranslates into an error in the posit on for emission. Further, thesemiconductor lasers 203 are mounted to the base 201 while the lensholders 207 and collimator lenses 3 are affixed to the flange 205. Afterthe adjustment of the optical characteristics, the aperture formingmember 209 is mounted. This brings about another problem that a scatterin the pitch of the two apertures 209 a results in an error in opticalcharacteristic after the mounting of the aperture forming member 209 andthereby lowers the beam pitch accuracy.

In light of the above, the seventh embodiment includes an elasticaperture forming member 25 implemented as, e.g., a plastic moldinghaving a generally U-shaped cross-section. The aperture forming member25 is mounted to the base 1 in such a manner as to embrace the opticalelement 5 positioned on the optical element support portion 23. A singleaperture 25 a is formed in the aperture forming member 25 because themember 25 is located downstream of the optical element 5 in thedirection of beam propagation. The aperture forming forming member 25includes opposite walls for retaining the optical element 5, asillustrated. The walls are formed with rib-like projections 25 b convextoward each other. The optical element support portion 23 is formed witha groove 23 c capable of mating with one of the projections 25 b. Thisconfiguration prevents the member 25 from easily slipping out of thebase 1 and increases the retaining force of the member 25.

In the illustrative embodiment, the aperture forming member 25 ismounted to the base 1 after the adjustment of the opticalcharacteristics of the base 1. This successfully maintains the initiallyset emission points with accuracy and prevents the member 25 fromeffecting the beam pitch. Moreover, the member 25 can be easilypositioned without resorting to any extra part. In addition, the pitchof the aperture and therefore the beam pitch accuracy is free from theinfluence of deformation of the case 9, so that the case 9 can beimplemented by an inexpensive plastic molding in order to reduce thecost of the light source device.

8th Embodiment

FIGS. 18-20 show an eighth embodiment of the present invention. Asshown, an aperture forming member 26 is molded integrally with theoptical member support portion 23 of the base 1. Two apertures 26 a areformed in the aperture forming member 26 such that they respectivelyalign with the centers of the collimator lenses 3. If desired, theaperture forming member 26 may be implemented as an independent memberand affixed to the optical support portion 23 by, e.g., adhesive.

The aperture forming member 26 is constructed integrally with the base 1and allows the optical characteristics to be adjusted on the basis ofthe beams passed through and shaped by the apertures 26 a. Thisguarantees the optical characteristics while absorbing errors in theaccuracy and positions of the apertures 26 a, thereby providing thelight source device with high accuracy. Furthermore, the apertureforming member 26 formed integrally with the base 1 reduces the numberof parts, and in addition the case 9 can be implemented by aninexpensive plastic molding. The resulting light source device is lowcost.

9th Embodiment

FIG. 21 shows a ninth embodiment of the present invention. As foroptical characteristics, a light source device is required to have thedirectionality (optical axis characteristic) and parallelism(collimation characteristic) of a laser beam to issue therefrom, asstated earlier. In practice, however, even if a collimator lens isbrought to a desired position, it is displaced due to, e.g., thecontraction of adhesive ascribable to curing and deformation ascribableto fastening. As a result, the optical characteristic after adhesion isextremely unstable. This embodiment solves this problem.

As shown in FIG. 21, the base 1 is fitted in the right end of the case9. The semiconductor lasers 2 and collimator lenses 3 are affixed to thebase 1. An aperture forming member 27 is formed with two apertures 27 aand implemented as a thin elastic plate. A lug 27 b is positioned at thecenter of the aperture forming member 27. A seat 9 a is formedintegrally with the case 9 and supports the bottom left edge of theoptical element or prism 5, as viewed in FIG. 21. The lug 27 b of theaperture forming member 27 elastically supports the intermediate portionof the right end of the element 5. A screw or adjusting means 28 extendsthroughout the wall of the case 9 and supports the top left portion ofthe element 5. The seat 9 a is a stationary fulcrum defining the centerof rotation. The adjusting means 28 should only be capable of finelyadjusting the angular position of the element 5 and is therefore notlimited to a screw.

Because the seat 9 a of the case 9 is flat, it is held in line-to-linecontact with the optical element 5. The element is therefore angularlymovable about the seat 9 a in a y-z plane (or about the x axis).

When the screw 28 is turned, its length within the case 9 varies andcauses the optical element 5 contacting the seat 9 a to rotate over asmall angle in the y-z plane. As a result, the distance between a firstreflection surface 5 a and a second reflection surface 5 b included inthe element 5 in the direction y is varied to, in turn, vary thedistance between the two beams 10 (pitch in the subscanning direction)in the direction y.

The angular movement of the optical element 5 varies only the distancebetween the beams 10 in the direction y, i.e., it does not effect theaccuracy in the direction x or the parallelism of each beam 10. That is,the rotation mechanism is capable of adjusting only the beam pitchwithout effecting the other optical factors. This is also true withthree or more beams.

The screw constituting the adjusting means 28 may be replaced with ascrew extending through the lug 27 b, in which case the aperture formingmember 27 will be formed of a material deformable little. To turn thescrew positioned at the lug 27 b, the base 1 may be formed with a holefor allowing a driver to be inserted toward the screw therethrough.

10th Embodiment

FIGS. 22-25 show a tenth embodiment of the present invention. In theconventional light source device discussed with reference to FIG. 2, theflange 205 and case 211 formed of metal and resin, respectively, arefastened together by the four screws 204. As a result, when thetemperature of the device rises, the flange 205 is caused to bend due toa difference in the coefficient of linear expansion between the twomaterials. Particularly, a bend in the beam pitch direction or directiony disturbs the parallelism of the individual beam; even the slightesterror in parallelism is critical because of the enlargement type optics.

Further, stresses in the directions x and y which are causative of theabove deformation are noticeably different in size and cause the flange205 to deform in combination. As a result, the flange 205 deforms in amore complicate manner. This, coupled with the fact that the deformationof the flange 205 depends on the rigidity of the same, causes the beampitch to vary in a complicate manner and results in defective images.This embodiment solves this problem.

As shown in FIGS. 22-25, a base 30 is made up of opposite mount portions30 a, an intermediate light source portion 30, and narrow bridgeportions 30 c respectively bridging the mount portions 30 a and lightsource portion 30 b. The semiconductor lasers 2 and collimator lenses 3are affixed to the light source portion 30. The base 30 is thereforeidentical with the base 1 of FIG. 7 except for the narrow bridgeportions 30 c. As for the rest of the construction, too, this embodimentis identical with the embodiment of FIG. 7.

Each bridge portion 30 c is positioned at the intermediate between anupper and a lower screw hole 30 formed in the adjoining mount portion 30a, and is coincident with the x axis direction. The bridge portions 30 care shown as being as thick as the mount portions 30 a and light sourceportion 30 b, but they may be thinner than them, if desired. In theillustrative embodiment, each mount portion 30 a is symmetrical in theup-and-down direction. Even when the mount portion 30 a is notsymmetrical in the above direction, the bridge portion 30 c shouldpreferably be positioned at the intermediate between the upper and lowerscrew holes 30 d.

Assume that the case 9 has a greater coefficient of linear expansionthan the base 30. Then, as shown in FIG. 24, an increase in ambienttemperature causes forces f1 and f2 to act on the front of the base 30in such a manner as to extend it in the directions x and y,respectively. However, only pulling forces f3 act on the light sourceportion 30 b via the bridge portions 30 c. Therefore, the base 30 isfree from the complicate bend stated earlier although its bridgeportions 30 c deform. Consequently, the bend of the light source portion30 b does no occur or occurs little in the directions x and y.Particularly, deformation in the direction y having noticeable influenceon the beam pitch is substantially obviated, so that the accurate beampitch is maintained.

While the illustrative embodiment includes two bridge portions 30 c, itmay include only one of them or three or more bridge portions inconsideration of limitations on the device or in matching relation to anapplication.

11th Embodiment

An eleventh embodiment of the present invention will be described withreference to FIG. 26. The base 1 and case 9 formed of aluminum andresin, respectively, are different in the coefficient of linearexpansion, as stated previously. This, coupled with the fact that thebase 1 and case 9 are fastened by the screws 11 at their four corners,causes the base 1 to bend when the ambient temperature rises. As aresult, the beam pitch is disturbed and brings about defective images.

In light of the above, this embodiment includes a back plate 31positioned at the side opposite to the case 9 with respect to the base1. The back plate 1 is formed of a material having substantially thesame coefficient of linear expansion as the material of the case 9, e.g,of the same material as the case 9. The back plate 1 is a rectangularplate having the same size as the base 1. Holes 31 a for the screws 11are formed in the four corners of the back plate 1 while two holes 31 bfor the semiconductor lasers 2 are formed at the center of the backplate 1.

The base 1 is sandwiched between the case 9 and the back plate 31substantially identical in size in the directions x and y and fastenedto them by the screws 11. When temperature around the light sourcedevice rises, the case 9 and back plate 31 having the same coefficientof linear expansion expand in exactly the same manner as each other. Thedeformations occurring at both sides of the base 1 cancel each other andcancel the deformation of the base 1 and prevent the base 1 frombending. This protects the beam pitch from disturbance.

If the case 9 and back plate 31 are noticeably different in bendingrigidity, then the base 1 may be caused to bend. In case of this kind ofbend, the bending rigidity of the back plate 31 should preferably besubstantially the same as the bending rigidity of the case 9.

12th Embodiment

Reference will be made to FIGS. 27, 28A and 28B for describing a twelfthembodiment of the present invention. FIG. 27 shows the configuration therear of the base 1. As shown, the two through bores 1 a are formed inthe center of the base 1. Annular ribs 1 e each surrounds the respectivebore 1 a on the rear of the base 1 for receiving the metallic flange ofthe semiconductor laser 2. In FIG. 28, two notches If are formed in eachrib 1 e on a line Y extending in the beam pitch direction (direction y)through the centers of the ribs 1 e.

The annular ribs 1 e have an inside diameter slightly smaller than theoutside diameter of the lasers 2. Each laser 2 is press-fitted in therespective bore 1 a while causing the notches 1 f to spread. Thereafter,the notches 1 f tend to restore their original positions and therebyincrease the retaining force acting on the laser 2. This insures theaccurate position of the laser 2.

The above configuration is satisfactory so long as each notch 1 fspreads evenly in the right-and-left direction due to the insertion ofthe laser 2. However, the spread of the notch 1 f is not always even inthe right-and-left direction. If the spread is not even in the abovedirection, then the center of the notch 1 f in the widthwise directionshifts and displaces the laser 2. In addition, the displacement is notconstant and cannot be estimated. The displacement in the direction ywould result in an error in beam pitch and therefore defective images.On the other hand, the displacement in the direction x does not bringabout any defective image only if the read timing is corrected. It istherefore desirable to limit the displacement to the direction x.

In the illustrative embodiment, as shown in FIG. 27, the two notches 1 fare formed in each rib 1 e face to face on the line Y extending in thebeam pitch direction (direction y) through the center of the rib 1 e.This configuration successfully limits the displacement to the directionx and thereby obviates the influence on the beam pitch ascribable to thedisplacement in the direction y.

FIGS. 28A and 28B each shows an alternative case in which a single notch1 f is formed in each rib 1 e. In this case, the spread of the notch 1 fcauses the rib 1 e to deform mainly in the direction opposite to thenotch 1 f and perpendicular to the widthwise direction of the notch 1 f,as indicated by an arrow. In light of this, as shown in FIG. 28A, thenotches 1 f should preferably be positioned only on one side (top) ofthe ribs 1 e on the line Y extending through the centers of the ribs 1e. Of course, the notches 1 f may be positioned only at the other side(bottom) of the ribs 1 e on the line Y. In this configuration, shifts inthe direction y occur in the same direction in the upper and lower ribs1 e and cancel each other, reducing the displacement in the direction y.

Alternatively, as shown in FIG. 28B, one notch 1 f may be positioned atthe bottom of the upper rib 1 e while the other notch 1 f may bepositioned at the top of the lower rib 1 e. This, however, causesdisplacements in the y direction to occur in opposite directions. Suchdisplacements would be added up and effect the beam pitch.

The notches 1 f of the ribs 1 e are capable of spreading without regardto the beam pitch direction. Therefore, the accuracy of the lasers 2 inthe beam pitch direction can be maintained.

13th Embodiment

FIGS. 29, 30 and 31A-31C show a thirteenth embodiment of the presentinvention also including the lens support portions 1 b each having anarcuate contact surface. The collimator lenses 3 each is affixed to thearcuate adhesion surface of the associated lens support portion 1 b bythe UV-curable adhesive layer 6, as described with reference to FIG. 8.However, the problem is that the coefficient of linear expansion of theadhesive layer 6 is far greater than the coefficient of linear expansionof the base 1 after the curing of the layer 6.

On the other hand, as shown in FIGS. 30 and 31A-31C, when thetemperature of the base 1 rises, the base 1 expands and increases thedistance L between the collimator lenses 3 by ΔL/2 outward of the base1. The adhesive layer 6 also expands, as indicated by a phantom line 6′in FIG. 31A. However, because the outward expansion of the adhesivelayer 6 is limited by the lens support portion 1 b, the layer 6 expandstoward the center of the collimator lens 3. Stated another way, thethickness of the adhesive layer 6 increases inward by ΔS. At thisinstant, if the center of the adhesive layer 6 is deviated from thecenter of the collimator lens 3 by δ, as shown in FIG. 31A, then theincrement ΔS of the thickness of the layer 6 due to expansion includes acomponent ΔS′ directed toward the center of the base 1, as shown in FIG.31B. That is, the adhesive layer 6 expands inward in the beam pitchdirection.

In FIG. 31C, the direction in which the distance L between thecollimator lenses 3 increases by ΔL (ΔL at each side) and the directionin which each lens 3 is displaced by ΔS′ in the direction y are oppositeto each other or cancel each other. Specifically, if the center of eachadhesive layer 6 is shifted outward of the base 1 by a suitable amount(e.g. δ), then the distance L between the collimator lenses 3 is equalto a value produced by subtracting the expansion component ΔS′ of theadhesive layer 6 in the direction y from the original expansion (ΔL/2).It is therefore possible to compensate for the expansion ascribable totemperature elevation and thereby confine the beam pitch accuracy in arequired range or fully prevent it from varying.

14th Embodiment

FIGS. 32 and 33 show a fourteenth embodiment of the present invention.Assume that the base 1 and case 9 are respectively formed of aluminumand resin, as stated with reference to FIG. 2. Then, when the lightsource is subjected to high temperature, the case 9 expands noticeablydue to a difference in the coefficient of linear expansion and causesthe base 1 to deform. This disturbs the beam pitch and thereby rendersimages defective.

In the illustrative embodiment, a case 33 is formed with slits 33 a atboth sides thereof. The slits 33 a reduce the bending rigidity of thecase 33. As a result, as shown in FIG. 33, even when the case 33 deformsdue to expansion, the deformation does not cause the base 1 to deform.Particularly, when the slits 33 a are formed in both sides of the case33 extending in the beam pitch direction, a bend in the direction y canbe effectively obviated. The embodiment therefore protects the beampitch from disturbance and thereby obviates defective images.

15th Embodiment

FIGS. 34A and 24B show a fifteenth embodiment of the present invention.The flange 205 and case 212 are fastened to each other by the fourscrews, as stated with reference to FIG. 2. This brings about a problemthat the thermal stress of the case 212 is transferred to the flange 205and causes the flange 205 to bend. This embodiment is a solution to thisproblem.

As shown in FIG. 34A, in the illustrative embodiment, three of the fourholes 1 d assigned to the screws 11 are implemented as elongate slots 1f. An elastic member 32 formed of, e.g., rubber is held between eachportion of the base 1 surrounding one slot 1 f and the screw 11 insertedin the slot 1 f so as to obviate shaking.

In the above configuration, the case 9 and base 1 are affixed to eachother at a single point and movable in the x-y plane within the range ofthe clearances between the other screws 11 and the slots 1 f. It followsthat even when the case 9 expands due to temperature elevation, the base1 is prevented from bending so long as the clearances are availablebetween the screws 11 and the slots 1 f. If desired, the slots 1 f maybe replaced with circular bores greater in diameter than the bore 1 d.

The accuracy required of the beam pitch is extremely high in thedirection y, but not so high in the direction x. In light of this, asshown in FIG. 34B, only two lower bores 1 d positioned side by side inthe direction x may be implemented as the elongate slots 1 f.

16th Embodiment

FIGS. 35A and 35B show a sixteenth embodiment of the present inventionincluding an elastic lug 34 formed of a plastic in place of the screw11. The lug 34 is molded integrally with the case 9 at the positionwhere the female screw is formed. The lug 34 is made up of a pluralityof (four in the embodiment) posts 34 a arranged in an annularconfiguration, lock pieces 34 b formed at the ends of the posts 34 a,and guide slants 34 c formed on the ends of the lock pieces 34 b. Thebase 1 is formed with the elongate slot 1 f. While the shank portion ofthe lug 34 constituted by the posts 34 a has a diameter smaller than helonger diameter of the slot 1 f, the head portion of the lug 34constituted by the lock pieces 34 b has a diameter greater than theshorter diameter of the slot 1 f.

The base 1 is mounted to the case 9 by the following procedure. Afterthe base 1 has been aligned with the case 9, each lug 34 of the case 9is inserted into the associated slot 1 f of the base 1. When the base 1is pressed against the case 9, the posts 34 a of the lug 34 elasticallybend inward at the same time due to the guide slants 34 c. As a result,the lug 34 is passed through the slot if until its lock portions 34 bprotrude to the other side of the base 1. As a result, the posts 34 aelastically restore their straight positions. In this condition, thebase 1 is prevented from separating from the case 9 because the lockportions 34 b have a greater diameter than the slot 1 f. In addition,the base 1 is biased against the case 9 due to the elasticity of thelock pieces 34 a. The base 1 and case 9 may be locked by the lug 34 atall of the four corners or at two or three of them; in the latter case,the lug 34 will be combined with the screw 11.

As described above, the third to sixteenth embodiments achieve thefollowing advantage. When the distance between the collimator lensesincreases in the beam pitch direction due to the thermal expansion ofthe base, the adhesive layer whose center is shifted outward expands insuch a manner as to cancel the expansion of the base. This successfullyreduces the displacement of the lenses in the beam pitch direction andthereby reduces the variation of the distance between the semiconductorlasers in the beam pitch direction.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. A light source assembly comprising: a base member including a base portion, a plurality of first fixing portions and a plurality of second fixing portions; a plurality of light source devices fixed to said base member; and a plurality of optical elements fixed to said base member and each including a side surface and a surface through which a light beam issuing from a particular one of said plurality of light source devices is transmitted; said plurality of first fixing portions being substantially equal in number to said plurality of light source devices, said plurality of light source devices each being fixed to a particular one of said plurality of first fixing portions such that a light beam issuing from the light source device is propagated in a preselected direction; said plurality of second fixing portions being substantially equal in number to said plurality of optical elements and located downstream of said plurality of first fixing portions in a direction of propagation of light beams issuing from said plurality of light source devices; said plurality of second fixing portions each including a support surface substantially identical in configuration with said side surface of an associated one of said plurality of optical elements, said support surface being substantially parallel to a direction of pitch of said light beams said direction of pitch being a direction perpendicular to the direction of propagation of the light beams through said plurality of optical elements, whereby a gap between said support surface of each of said plurality of second fixing portions and an associated one of said plurality of optical elements is substantially uniform to allow adhesive filling said gap to be uniformly cured.
 2. A light source assembly as claimed in claim 1, wherein said plurality of second fixing portions are formed substantially integrally with said base portion.
 3. A light source assembly as claimed in claim 2, wherein said base member further comprises a third fixing portion located downstream of said plurality of first fixing portions in the direction of propagation of the light beams.
 4. A light source assembly as claimed in claim 3, further comprising: an aperture member formed with a plurality of apertures and including an aperture surface configured to shape the light beams by passing said light beams through said apertures.
 5. A light source assembly as claimed in claim 1, wherein said support surfaces of said plurality of second fixing portions are symmetrical with respect to a line perpendicular to the direction of pitch of the light beams.
 6. A light source assembly as claimed in claim 1, wherein said side surface of each of said plurality of optical elements is cylindrical, and wherein said support surface of each of said second fixing portion has an arcuate section having a greater diameter than said side surface.
 7. A light source assembly as claimed in claim 6, wherein the arcuate section of said support surface is smaller than a semicircle.
 8. A light source assembly as claimed in claim 1, wherein said plurality of optical elements each comprise a lens and said light source assembly further comprises: a prism located downstream of said plurality of optical elements in the direction of propagation of said light beams, wherein said prism varies a pitch of the light beams and includes a side surface and a surface through which said light beams are transmitted.
 9. A light source assembly as claimed in claim 8, wherein said base member further includes a third fixing portion located downstream of said plurality of second fixing portions in the direction of propagation of the light beams and including a fixing surface facing said side surface of said prism and configured to fix said prism to said base member.
 10. A light source assembly as claimed in claim 9, wherein said fixing surface of said third fixing portion is substantially parallel to each support surface of said plurality of second fixing portions.
 11. A light source assembly as claimed in claim 1, wherein said plurality of optical elements each comprise a lens and said light source assembly further comprises: a prism located downstream of said plurality of optical elements in a direction of propagation of said light beams, wherein said prism varies a pitch of the light beams and includes a side surface and a surface through which said light beams are transmitted; and an aperture member formed with a plurality of apertures corresponding to said plurality of light beams.
 12. A light source assembly as claimed in claim 11, wherein said aperture member includes an aperture surface and retaining surfaces facing opposite side surfaces of said prism, respectively, and wherein the light beams are transmitted through said aperture surface and shaped thereby.
 13. A light source assembly as claimed in claim 12, wherein said base member further includes a third fixing portion located downstream of said plurality of second fixing portions in the direction of propagation of the light beams and including a fixing surface facing one of said side surfaces of said prism and configured to fix said prism to said base member, and wherein said retaining surfaces of said aperture member retain said third fixing portion and said prism after said prism has been fixed to said third fixing portion.
 14. A light source assembly as claimed in claim 1, wherein said plurality of first fixing portions each is cylindrical and formed with a through bore configured to receive a respective one of said plurality of light source devices and a notch extending in the direction of pitch of the light beams.
 15. A light source assembly as claimed in claim 1, wherein said plurality of optical elements each comprise a lens and said light source assembly further comprises: a prism located downstream of said plurality of optical elements in the direction of propagation of said light beams, wherein said prism varies a pitch of the light beams and includes opposite face surfaces through which said light beams are transmitted; an aperture member formed with a plurality of apertures corresponding to said plurality of light beams; and a case matable with said base member and adapted to receive said lens, said aperture member, and said prism in substantial alignment therein.
 16. A light source assembly as claimed in claim 15, further comprising means for adjusting the position of said prism within said case thereby varying the pitch of said plurality light beams.
 17. A light source assembly as claimed in claim 16, wherein said aperture member includes an aperture surface facing a first of said opposite face surfaces of said prism wherein the light beams are transmitted through said aperture surface and shaped thereby, said aperture surface including a lug configured to provide a compression force against said first of said opposite face surfaces of said prism, and wherein said base member includes a seat for contacting an edge of said prism and defining an axis of rotation of said prism, and an adjustment port for receiving an adjustment screw, said adjustment screw moveably contacting a second of said opposite face surfaces so as to provide an opposing force to said compression force, wherein adjustment of said screw rotates said prism about said axis of rotation to vary the pitch of said plurality of light beams.
 18. A light source assembly, comprising: a base member comprising first and second base portions; a plurality of light source devices fixed to said base member; and a plurality of optical elements fixed to said base member and each including a side surface and a surface through which a light beam issuing from a particular one of said plurality of light source devices is transmitted; said first base portion including at least one first fixing portion configured to fix at least one of said plurality of light source devices to said first base portion, at least one second fixing portion located downstream of a respective first fixing portion in a direction of propagation of the light beams and configured to fix at least one of said plurality of optical elements to said first base portion, and a third fixing portion configured to fix said second base portion, to said first base portion, each said second fixing portion each including a surface being substantially identical in configuration with said side surface of an associated one of said plurality of optical elements for allowing adhesive to be uniformly cured thereon; said second base portion including at least one fourth fixing portion configured to fix at least one of said plurality of light source devices to said second base portion, and at least one fifth fixing portion located downstream of a respective fourth fixing portion in the direction of propagation of the light beams and configured to fix at least one of said plurality of optical elements to said second base portions, each said fifth fixing portion each including a surface substantially identical in configuration with said side surface of an associated one of said plurality of optical elements for allowing adhesive to be uniformly cured thereon.
 19. An apparatus for scanning a light-sensitive device movable in a subscanning direction relative to a light beam, said apparatus comprising: a base member including a plurality of first fixing portions and a plurality of second fixing portions; a plurality of light source devices arranged in the subscanning direction, each configured to emit a respective light beam; a plurality of optical elements arranged in the subscanning direction and each including a side surface and a surface through which the light beam issuing from an associated one of said plurality of light source devices is transmitted; and a deflecting device configured to deflect in a main scanning direction the light beams transmitted through said plurality of optical elements; said plurality of first fixing portions being substantially equal in number to said plurality of light source devices, said plurality of light source devices each being fixed to a particular one of said plurality of first fixing portions such that a light beam issuing from the light source device is propagated in a preselected direction; said plurality of second fixing portions being substantially equal in number to said plurality of optical elements and located downstream of said plurality of first fixing portions in a direction of propagation of light beams issuing from said plurality of light source devices; said plurality of second fixing portions each including a support surface substantially identical in configuration with said side surface of an associated one of said plurality of optical elements, said support surface being substantially parallel to a direction of pitch of said light beams, said direction of pitch being a direction perpendicular to the direction of propagation of the light beams, whereby a gap between said support surface of each of said plurality of second fixing portions and an associated one of said plurality of optical elements is substantially uniform to allow adhesive filling said gap to be uniformly cured.
 20. An apparatus as claimed in claim 19, wherein said plurality of optical elements each comprise a lens, and said apparatus further comprises: a prism located downstream of said plurality of optical elements in a direction of propagation of said light beams, wherein said prism varies a pitch of the light beams and includes a side surface and a surface through which said light beams are transmitted.
 21. An apparatus as claimed in claim 20, wherein said base member further includes a third fixing portion located downstream of said plurality of second fixing portions in the direction of propagation of the light beams and including a fixing surface facing said side surface of said prism and configured to fix said prism to said base member.
 22. An apparatus as claimed in claim 21, wherein said fixing surface of said third fixing portion is substantially parallel to each support surface of said plurality of second fixing portions.
 23. An apparatus as claimed in claim 19, wherein said plurality of optical elements each comprise a lens and said apparatus further comprises: a prism located downstream of said plurality of optical elements in a direction of propagation of said light beams, wherein said prism varies a pitch of the light beams and includes a side surface and a surface through which said light beams are transmitted; and an aperture member formed with a plurality of apertures corresponding to said plurality of light beams.
 24. An apparatus as claimed in claim 23, wherein said aperture member includes an aperture surface and retaining surfaces facing opposite side surfaces of said prism, respectively, and wherein the light beams are passed through said aperture surface and shaped thereby.
 25. An apparatus as claimed in claim 24, wherein said base member further includes a third fixing portion located downstream of said plurality of second fixing portions in the direction of propagation of the light beams and including a fixing surface facing one of said side surfaces of said prism and configured to fixing said prism to said base member, and wherein said retaining surfaces of said aperture member retain said third fixing portion and said prism after said prism has been fixed to said third fixing portion.
 26. An apparatus as claimed in claim 19, wherein said light sensitive device comprises a photoconductive element.
 27. An apparatus as claimed in claim 19, wherein said deflecting device comprises a polygonal mirror.
 28. In a structure for mounting a plurality of light source devices configured to emit light beams to a base member, said base member includes a plurality of fixing portions substantially equal in number to said plurality of light source devices and each being cylindrical and formed with a through bore for inserting a particular one of said plurality of light sources devices, said plurality of fixing portions each including a notch extending in a direction of pitch for the light beams thereby limiting displacement of said light source to a direction other than said direction of pitch.
 29. An apparatus adapted to adjust a pitch between a plurality of light sources of a light source assembly in an image forming apparatus, said light source assembly including a plurality of light source devices and a plurality of optical devices mounted to a base member, comprising: a prism having opposite face surfaces through which said light beams are transmitted; an aperture member including an aperture surface facing a first of said opposite face surfaces of said prism wherein the light beams are transmitted through said aperture surface and shaped thereby, said aperture surface including a lug configured to provide a compression force against said first of said opposite face surfaces of said prism; and a case matable with said base member and adapted to receive said lens, said aperture member, and said prism in substantial alignment therein and including a seat for contacting an edge of said prism and defining an axis of rotation of said prism, and an adjustment port configured to receive an adjustment screw, said adjustment screw moveably contacting a second of said opposite face surfaces so as to provide an opposing force to said compression force, wherein adjustment of said screw rotates said prism about said axis of rotation to vary the pitch between said plurality of light beams.
 30. A method of varying a pitch between a plurality of light sources of a light source assembly in an image forming apparatus, said light source assembly including a plurality of light source devices and a plurality of optical devices mounted to a base member, comprising: transmitting said plurality of light beams through a prism having opposite face surfaces through which said light beams are transmitted; providing an aperture member including an aperture surface facing a first of said opposite face surfaces of said prism wherein the light beams are transmitted through said aperture surface and shaped thereby, said aperture surface including a lug configured to provide a compression force against said first of said opposite face surfaces of said prism; and mating a case with said base member to contain said prism and aperture therein, said case including a seat for contacting an edge of said prism and defining a center of rotation of said prism, and an adjustment port configured to receive an adjustment screw, said adjustment screw contacting a second of said opposite face surfaces so as to provide an opposing force to said compression force, turning said adjustment screw to vary the inclination of said prism relative to said center of rotation thereby adjusting the pitch between said beams transmitted through said prism.
 31. A light source assembly comprising: a base member; a plurality of light source devices; a plurality of optical elements; means for fixing said plurality of light source devices to said base such that a light beam issuing from each light source device is propagated in a preselected direction; means for adhering said plurality of optical devices to said base downstream of said light source devices in a direction of propagation of the light beams, such that contraction of an adhesive for said means for adhering has directionality substantially along a single axis.
 32. A light source assembly as claimed in claim 31 wherein said directionality of said contraction is perpendicular to a pitch direction of said plurality of light beams.
 33. A light source assembly, comprising: a base member made up of a first and a second base portion; a plurality of light source devices; a plurality of optical elements; means for fixing at least one of said plurality of light source devices to said first base portion, means for adhering at least one of said plurality of optical elements to said first base portion, such that contraction of an adhesive used for said means for adhering has directionality substantially along a single axis; means for fixing at least one of said plurality of light source devices to said second base portion; means for adhering at least one of said plurality of optical elements to said second base portion, such that contraction of an adhesive used for said means for adhering has directionality substantially along a single axis; means for adjustably attaching said second base portion, to said first base portion.
 34. A light source assembly as claimed in claim 33 wherein said directionality of said contraction is perpendicular to a pitch direction of said plurality of light beams.
 35. A light source assembly as claimed in claim 34 wherein said means for a adjustably attaching includes means for adjusting said second base portion in said pitch direction relative to said first base portion.
 36. An apparatus for scanning a light-sensitive device movable in a subscanning direction relative to a light beam, said apparatus comprising: a base member; a plurality of light source devices arranged in the subscanning direction, each configured to emit a respective light beam; a plurality of optical elements arranged in the subscanning direction and each including a side surface and a surface through which the light beam issuing from an associated one of said plurality of light source devices is transmitted, and means for deflecting in a main scanning direction the light beams transmitted through said plurality of optical elements; means for fixing said plurality of light source devices to base member such that a light beam issuing from the light source device is propagated in a preselected direction; means for adhering said plurality of optical elements to said base member located downstream of said plurality of light source devices in a direction of propagation of light beams issuing from said plurality of light source devices, such that contraction of an adhesive for said means for adhering has directionality substantially along a single axis.
 37. An apparatus as claimed in claim 36 wherein said directionality of said contraction is perpendicular to a pitch direction of said plurality of light beams.
 38. A light source device comprising: a plurality of semiconductor lasers; means for press fitting said semiconductor lasers to a base; a plurality of collimator lenses; means for adhering said plurality of collimator lenses to said base via an adhesive layer such that thermal expansion of said adhesive layer cancels out in a direction of pitch of said plurality of semiconductor lasers; means for combining said laser beams output from said collimator lens; and a case mounted to said base and adapted to cover said plurality of collimator lenses and said optical element. 